The Nef allele encoded by the simian immunodeficiency virus (SIV) strain smmPBj14 contains an immunoreceptor tyrosine-based activation motif (ITAM) that interacts with zAP-70 and Syk, and activates intracellular signalling. It is hypothesized that SIVsmmPBj14 Nef may also be capable of stimulating dendritic cells (DC), and that this may enhance antigen presentation by DC. In aim 1, recombinant adenovirus vectors (rAV) will be used to express the following proteins in DC: (1) wild-type SIVsmmPBj14 Nef, (2) a Y17R mutant, which lacks the ITAM, and (3, 4) truncated mutants which contain only amino acids 1-43 of either wild type or YR mutant Nef (this region includes the intact ITAM). After infection of DC with these vectors, intracellular signaling events and modification of key protein substrates will be examined. In aim 2, Nef-expressing rAV will be used to infect cultured DC, and the efficiency with which these cells can stimulate an antigen-specific T cell response will be measured. Finally, an rAV construct which co-expresses HIV-1 gp120 and SIVsmmPBj14 Nef (or its ITAM) will be constructed, and inoculated into BALB/c mice; T cell responses to gp120 will be measured. This will reveal whether SIVsmmPBj14 Nef, or its ITAM, can enhance the immunogenicity of an HIV-1 vaccine.